Heavy Weight Drill Pipe
As the name suggests, the Heavy Weight Drill Pipe (HWDP) is tubular with drill pipe dimensions but has a heavier wall. It is used as the intermediate member of the drill string between drill collars and drill pipes. HWDP usually has longer tool joints than drill pipe. Its weight is less than the drill collar but more than the drill pipe. Having HWDP in the drill string has multiple advantages. It reduces the required number of drill collars in the string while maintaining the drill string's ability to apply the required weight on the bit for drilling. It has less wall contact than drill collar which reduces torque and the chances of differential sticking. HWDP provides smooth weight transition from drill collars to drill pipes and can be run through the hole angle much easily due to less rigidity.